The postal company, part of International Distributions Services Plc, said it had also resumed exports of letters and from 1900 GMT customers could begin submitting international export letters to its network.
The websites of the central bank and Bankdata, a company that develops IT solutions for the financial industry, were hit by DDoS attacks, which direct traffic toward targeted servers in a bid to knock them offline.
A Russian hacking team known as Cold River targeted three nuclear research laboratories in the United States this past summer, according to internet records reviewed by Reuters and five cyber security experts.
The issue affected customer information such as name, contact information, date of birth, hashed Social Security number, account identifiers and information related to transactions with BetMGM, the company said.
The official Vatican website was taken offline on Wednesday following an apparent hacking attack, the Holy See said. "Technical investigations are ongoing due to abnormal attempts to access the site," Vatican spokesman Matteo Bruni said.
Thousands of smartphone applications in Apple and Google's online stores contain computer code developed by a technology company, Pushwoosh, that presents itself as based in the United States but is actually Russian, Reuters has found.
Australia's Home Affairs Minister Clare O'Neil on Sunday said the government would consider making illegal the paying of ransoms to cyber hackers, following recent cyber attacks affecting millions of Australians.
The White House will host officials from 37 countries and 13 global companies in Washington this week to address the growing threat of ransomware and other cybercrime, including the illicit use of cryptocurrencies, a senior U.S. official said.
The company said it took "immediate steps to contain the incident, and engaged specialized cybersecurity firms", adding that there was no evidence that any sensitive data, including customer data, had been accessed at this stage.